Radiation-induced middle ear and mastoid opacification in skull base tumors treated with radiotherapy

Purpose: To assess the incidence of middle ear (ME) pathology in patients treated with radiotherapy (RT) for skull base tumors. Methods and Materials: A retrospective analysis of 61 patients treated with RT between 2003 and 2008 for skull base tumors was conducted. Clinical outcomes and demographics were reviewed. Dose-volume histogram analysis was performed on the eustachian canal (EC), ME, mastoid air cells, vestibular apparatus, cochlea, internal auditory canal, lateral and posterior nasopharynx, and temporal lobes to relate doses to symptoms and radiographic change. Otomastoid opacification was rated 0 (none), 1 (mild), 2 (moderate), and 3 (severe) by a neuroradiologist blinded to clinical outcomes and doses. Results: The median prescribed dose was 50.4 Gy (range, 14-74 Gy). The ME mean dose was 14 Gy and 34 Gy for Grade 0-1 and 2-3 opacification, respectively (p < 0.0001). The mean mastoid dose was 10 Gy and 26 Gy for Grade 0-1 and 2-3, respectively (p < 0.0001). The mean EC dose was 17 Gy and 32 Gy for Grade 0-1 and 2-3, respectively (p = 0.0001). Otomastoid opacification resolved in 17 of 40 patients (42.5%), at a mean of 17 months after RT (range, 2-45 months). Otomastoid opacification persisted in 23 of 40 patients (57.5%), with a mean follow-up of 23 months (range, 2-55 months). Multivariate analysis showed that mastoid dose >30 Gy (odds ratio = 28.0, p < 0.001) and posterior nasopharynx dose of >30 Gy (odds ratio = 4.9, p = 0.009) were associated with Grade 2-3 effusions, whereas other factors including dose to EC and ME were not significant. Conclusions: A mean RT dose >30 Gy to the mastoid air cells or posterior nasopharynx is associated with increased risk of moderate to severe otomastoid opacification, which persisted in more than half of patients at 2-year follow-up.